This invention relates to a dental handpiece and, more particularly, to a device for preventing intrusion of foreign matter, such as cut tooth particles or chips to a bearing section within the dental handpiece.
A straight type of the currently used dental handpiece is shown as an example in FIG.5.
A main body of a dental handpiece C is constituted by a sheath section 10, a gripper section 11 and a nose section 12 provided at the middle, at the rear part and at the foremost part of a shell, respectively. Within the inside of the main body of the dental handpiece C, a spindle 2 connected to a driving motor, not shown, by means of a coupling 1, is rotatably supported for rotation by a forward side bearing 3 and a rear side bearing 4. A cylindrical pin-thrusting pipe 6 having a tapered forward end face 6a is slidably disposed on the outer periphery of the spindle 2 and is perpetually biased by a chuck spring 5 in a direction towards the foremost part of the handpiece C. Under the force of the chuck spring 5, the tapered face 6a abuts on a projection 7a of each of a plurality of bur-thrusting pins 7 for radially thrusting the bur-thrusting pins 7. A dental tool 9, introduced at a tool inserting opening 8, is clamped under the thrusting force exerted by the bur-thrusting pins 7 arranged on its periphery so as to be received and secured within the spindle 2.
With the above described dental handpiece C, the rotating spindle 2 is supported by bearings 3, 4 secured to the main body, so that there is necessarily provided a clearance to permit rotation of the spindle 2 between the main body and the rotating spindle 2.
On the other hand, it is known that, when the spindle 2 is rotated within the inside of the handpiece C, the air therein is stirred to induce a flow of air to lower the air pressure within the inside of the handpiece C as compared to the outside air pressure. The result is that a foreign matter, such as fine cut particles or chips of tooth, tends to be sucked into the inside of the handpiece C by way of a gap at the foremost part of the handpiece C between the tool inserting opening 8 and the dental tool 9. Such foreign matter may ultimately be charged in an inner gap 13 delimited between the nose section 12, the dental tool 9 and the foremost part of the spindle 2 to cause balls or a retainer of the forward side bearing 3 to wear or injure the ball race thereof.